Project Number: 1265-12130-002-06
Project Type: Specific Cooperative Agreement

Start Date: Aug 10, 2005
End Date: Jun 30, 2009

Objective:
Measure stable isotopes of N and O to investigate the sources and fates of nitrate in agricultural watersheds and riparian buffers.

Approach:
We will analyze the abundance of 15N and 18O in nitrate from streams and groundwater, comparing steams draining several agricultural watersheds with differing land use, and comparing groundwater from transects running from crop fields through adjacent riparian buffers. As nitrate is consumed by denitrification, 15N and 18O abundances increase in the unconsumed nitrate. Nitrate originating from animal waste is richer in 15N than is nitrate originating from inorganic fertilizers. Therefore, the 18O content reflects denitrification while the 15N content reflects both denitrification and the relative importance of animal waste sources of nitrate nitrogen. Comparing the isotopic composition in nitrate from different streams will provide an indication of the watershed-scale effects of denitrification and animal waste applications. Comparing the isotopic composition in groundwater in riparian buffers will provide an indication of how much nitrate is removed by denitrification as groundwater from croplands flows through the buffers.